Electric-heating resistance element



L. V. LEONARD.

ELECTRIC HEATING RESISTANCE ELEMENT.

APPUCATION FILED APR. 5, 1919.

Patented Apr. 20,1920.

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LESLIE VICTOR LEONARD, OF RICHMOND, VICTORIA, AUSTRALIA.

ELECTRIC-HEATING RESISTANCE ELEMENT.

Specification of Letters Patent.

Patented Apr. 20, 1920.

Application filed April 5, 1919. Serial No. 287,867.

To all whom it may concern:

Be it known that I, LnsLm VICTOR LEON- ARD, a subject of the King of Great Britain, of 619 Bridge road, Richmond, in the State of Victoria, Australia, have invented'certain new and useful Improvements in Electric- Heating Resistance Elements of which the following isa specification.

Consequent upon the extended uses to which electric heat is being applied in numerous manufactures resulting to some extent from the decreasing supply cost of this form of energy, considerable attention has been given to the form and manufacture of the heat-resisting flexible wire constituting the high resistance element to the passageof the current.

This element has undoubtedly reached a high efficiency in itself but the means and methods at present employed for mounting same and effecting terminal connections are capable of material improvement. It is known to wind the resistance element about a porcelain or similar support or base in a helical groove and that consequent upon repeated heating and cooling the wire coils become expanded beyond the retaining groove and slip down the base causing short circuiting of the contacting coils with resulting reduction of the resistance. Further the circuit terminals to which the ends of the wire element are attached are usually constituted of ordinary commercial metal such as brass and at the actual point of contact a hot spot is formed in the wire which after a short period of time usually causes break down at that point. Another disability in the existing apparatus in which a plurality of elements are provided. as for instance in radiators is that it is a matter of some difiiculty to remove and replace burnt out sections of the apparatus.

The disabilities in existing appliances above noted are eliminated by the present invention, a practical application of which is hereinafter described with reference to the accompanying drawings. I

Briefly stated the base of the element manufactured of the usual material such as porcelain, fused silica or like heat resisting insulating material, is preferably of tubular form having the usual exterior groove of continuous helical form the resistance wire beingwound therein and according to this invention two lengths of the wire are twisted together and a short length of same at each end is electrically associated with a resistance element of lower resistance value. The associated high and low resistances terminate together in the contact piece which according to this invention is attached to the base as by a short through bolt, being of angular form with its outer or free end pro-,

vided with a clean surfaced through aperture capable of making an effective slip-on electrical contact with a pin terminal mounted in the base of the apparatus. The pin terminals may be cylindrical or slightly tapered from the base outwardly with the element terminals to correspond and preferably the first mentioned terminals project from integral plates upon the upper surface of which bears the lower surface of the element terminal.

In the drawings Figure 1 is a plan view with portions removed for convenience in appreciating detail of construction;

Fig. 2 being a section on line plane 11-11 in Fig. 1;

Fig. 3 is an enlarged side elevation illustrating only the method of effecting the terminal connection of the resistance wire; and

Fig. 4 is a view provided for the purpose of explaining a method of associating the resistance wire with a flexible wire resistance of lower value.

The pair of tubular bases 6 illustrated in Fig. 1 indicate a known radial arrangement of a plurality of same.

The pin contacts or terminals 7 on which the bases are supported project from metallic plates 8 two of which are connected to the leading in supply conductors as by means of a downward extension 8 screw threaded to receive a milled nut 8".

In the arrangement shown the elements constitute two sets of three in number with each set wired in series with the supply current. Eachv set may be separately switch controlled for controlling the volume of the apparatus from full to half capacity. Fur ther as each element is of equal resistance value one spare element is sufficient to re place any one element which breaks down.

T he usual helical groove is formed in the exterior surface of each base 6 to receive the wire resistance 9 which latter to accord with this invention is formed of two lengths closely twisted together, the turning ofthc wires about each other creating spaces between the successive kinks which while allowing for effective expansion prevents the wires from leaving the retaining groov and possibly, as far as applicants observation indicates, tends to tighten up the coils.

The resistance wire 9 is for a short distance from each end intertwined with a short length of resistance wire 9 of lower resistance value. This intertwining ot' the high and low resistance wires 9 and 9 re spectively may be accomplished by bending the low resistance wire and then bringing its ends parallel with the end of the high resistance wires 9 as in Fig. 4 and finally twisting all the wires closely together to make effective contact with the surfaces. The intertwined ends of the high and low resistance wires are then secured to a termi nal as for instance by inserting the combined ends into the aperture in the terminal T and fixing same by a binding screw 10. As a result of this arrangement the temperature of the terminal portion of the wires 9 does not rise to the temperature of the portion around the basc6 and consequently the damage usually resulting from the. usual terminal connection is obviated and the life of the terminal T increased. The terminals T are of angular form one limb having one surface curved to correspond to the inner diameter of the base 6 (see Fig. 1) and held. thereto by a screw 11. The other limb of the terminal T ends with an eye T to receive with an accurate fit one of the pin contacts 7.

The pin contacts 7 and plates 8 are shown mounted on a disk 12 of non-conducting material and a central hole 13 is provided therein for the through passage of an elongated pin 14 on which is also mounted a hood plate 15 of material similar to the disk 12. This plate 15 is held in position by thumb screw 16 and has its outer edge flanged downwardly and provided with a series of scallops 17 to receive a portion of the inclined tubular bases (3 the screw 16 when in its normal position causing the plate 15 to bear down on the latter and maintain the underneath plane surface of the eyes T in surface contact with the plates 8. A convenient method for connecting the outer end of the wires 9 and. 9 to the terminals T is shown on the drawings and consists in passing same through an aperture 18 in the base 6 and down through the center of the latter. It will readily be seen that by raising the hood plate 15 clear of the bases 6 any one of the latter can be instantly removed and as readily placed in position. The dis tance piece 19 bridging each pair of terminals T attached to one base 6 is of nonconducting material being held in place by the screws 10 and assures the maintenance of the correct position of the terminals rela tive to the pin contacts 8.

It is to be clearly understood that the particular arrangement of the parts described with reference to the accompanying drawings is not essential to the carrying out of the present invention as same may be modified to meet differing requirements in practice.

I claim 1. In an electric heating unit, in combination, a base of non-conducting material having an exterior helical groove, and a resistance element formed of wires closely twisted together and wound in said groove.

2. In an electric heating unit the combination of a terminal, a high resistance wire engaged by said terminal, and an element of lower resistance than said wire associated with. the portion of said wire engaged by said terminal and extending along a part only of the length of said high resistance wire.

3. In an electric heating unit the combination of a terminal, a high resistance wire engaged by said terminal and a low resistance wire shorter than said high resistance wire and intertwined with the portion of said high resistance wire engaged by said terminal.

4. An electric heating unit consisting of a base of non-conducting material, an exterior helical groove therein, a high resistance element formed of twisted wires wound in said groove, an element of lower resistance shorter than and terminally associated with said high resistance element and a terminal to which said terminal combination of high and low resistance wires are connected.

5. An electric heating apparatus consisting of a series of radially arranged tubes to which are attached a pair of terminals for the resistance wire, said terminals each having a terminal eye adapted to receive a pin contact.

6. An electric heating ,unit consisting of a tubular base having an exterior helical groove in which is embedded a resistance wire in combination with a pair of terminals for said wire of angular form, one limb of each terminal being attached to said tubular base and the other projecting from the lower end of the base and having a terminal eye to receive a pin contact.

7. An electric heating unit consisting of a series of radially arranged tubes of nonconducting material each having an exterior helical groove, a high resistance element formed of closely twisted wires embedded in said groove, a low resistance element intertwined for some distance with each end of said high resistance element, a pair of terminals for the ends of said combined high and low resistance elements, said terminals adapted to fit a plain pin contact.

8. In an electric heating unit, the combination of a support of refractory nonconducting material, a high resistance wire wound on said support, low resistance wires associated with the end portions of said high resistance wire, said low resistance wires having no electrical connection with one another except through said high resistance Wire, and terminals respectively engaging the associated portions of said wires.

9. In an electric heater, a support of insulating refractory material and a high resistance conductor wound on said support, said 10 conductor being formed of Wires so twisted together as to allow for the expansion of the conductor without loosening its engagement with the support.

LESLIE VICTOR LEONARD. 

